This invention relates to an improved shaft seal for a rotary shaft extending from a container containing agitated abrasive particulate solids through a wall of the container.
In the operation of copier/duplicator machines, a conductor film is used to transfer an image from an original to a copy. The photo-conductor film is initially charged at a corona charger or the like and then passed to an imaging section where a charged image is placed on the conductor film. The film then passes to a section where a developer and toner are used to deposit a the toner on the charged image. In this section the developer, which is a finely divided magnetic metallic oxide such as iron oxide, becomes associated with toner which is then passed into close proximity to the conductor film which attracts the toner to the charged image. The developer and toner are retained in a developer sump, which includes a rotary blender, optionally a rotary bucket shell and a rotary toner shell or the like, which move the blend of toner and developer into proximity to the photo-conductor film. These components are powered by shafts extending through the wall of the container of developer and toner. The developer is a particularly abrasive material and it has been difficult to develop seals which will provide extended life to bearings and other components used to provide power to the blender, bucket shell, toner shell or the like inside the developer/toner sump.
The failure of these bearings is particularly serious since they are not readily replaced in the field by a service representative. Since these bearings cannot be replaced in the field, they require replacement of the entire sump when bearing failures occur. Further the escape of developer and toner can result in the presence of undesired contaminants in the copier/duplicator machine.
Accordingly a continuing search has been directed to the development of improved seals for such shafts.
According to the present invention, an improved seal for a shaft extending from a container containing agitated abrasive particulates through a wall of the container is provided by a seal comprising: a polymeric first washer member having a first side and a second side and sealingly positioned at its first side against the wall of the container and sealingly positioned around the shaft for rotation of the shaft inside the first washer member; a polymeric second washer member having a first side and a second side and sealingly positioned around the shaft with its first side in contact with the second side of the first member for rotation of the second member with the shaft and for rotation of the first side of the second member relative to the second side of the first member; a polymeric compressible foam third washer member having a first side and a second side and sealingly positioned around the shaft with its first side in contact with the second side of the second member for rotation with the shaft and the second member; and, a retaining member having a first side and a second side and positioned at least partially around the shaft in a groove in the shaft with its first side in engagement with the second side of the third member for rotation with the shaft and the third member, the groove being positioned to retain the first member, the second member and the third member in compression between the retaining ring and the wall of the container.